Robustness of topological edge states in alternating spin chains against environment

Abstract

Both the Haldane spin-$1$ chain and dimerized chains of spin-$1/2$ exhibit topologically protected edge states that are robust against specific perturbations. Recently, such spin chains have been specifically assembled on surfaces and we investigate here the robustness of these edge states against coupling to the surface. Since no physical system can be considered perfectly isolated, it is crucial to examine whether topological robustness is maintained in the presence of environmental coupling. We apply exact diagonalization to a Lindblad master equation that couples an alternating Heisenberg spin chain based on spins $1/2$ to a surface via various jump operators. The robustness of topological states is assessed via the time evolution of quantities such as the ground-state degeneracy, correlation function, entropy, and magnetization of edge states. We investigate chains built from dimers with antiferromagnetic and ferromagnetic intra-dimer coupling, which resemble Su-Schrieffer-Heeger and the Haldane models, resp., and assess the impact of $z$-axis anisotropy and longer-ranged couplings. Generally, we find that signatures of topological properties are more robust in Su-Schrieffer-Heeger-like chains than in Haldane-like chains.